Air warming system for providing a controlled temperature of air to an air blanket

ABSTRACT

A fluid blanket warming system for a patient includes a thermal blanket unit for receiving heated gas through a coupling port. A portable heat source includes a heater unit and a blower unit that are controlled by a control circuit for providing a desired output of temperature to a patient. A flexible conduit delivers the heated gas from the heat source to the thermal blanket. A temperature sensor unit can be mounted adjacent the thermal blanket unit and in contact with the gas received from the heater unit to provide a temperature signal representative of the heated gas. The temperature sensor unit can be mounted directly on the thermal blanket, on the coupler of the flexible conduit, or on a modular coupler to provide a temperature signal to the control circuit.

This is a continuation of U.S. Ser. No. 09/113,630, filed on Jul. 10,1998, now U.S. Pat. No. 6,143,020.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an air blanket warming system forincorporating a remote temperature sensor mounted adjacent the airblanket to provide a temperature signal representative of the heated airdelivered to the air blanket and includes an improved conduit unit,remote temperature sensor unit, and improved air blanket.

2. Description of Related Art

It is well known to provide heated air to portions of the human body tomaintain the human body temperature and/or to provide curative heattreatment to a patient. Air blankets are frequently used in operatingrooms and critical care units and include a disposable air blanket thatcan be formed from a thin plastic or thin plastic paper configurationwith appropriate apertures on one side of the blanket to bathe a patientwith warm air. During the operation, the temperature of the patient cantherefore be controlled. In a post-operative setting, it is possible totreat the patient for hypothermia. The concepts and use of theapplication of both heated and cold air is well known such as shown inU.S. Pat. No. 2,110,022 and U.S. Pat. No. 2,601,189.

Air blankets or thermal blankets generally use a heater unit that isportable and includes a cabinet having operator controls for settingtemperatures with an internal heater unit and blower unit for deliveringa controlled temperature of air to a flexible conduit. The flexibleconduit extends from the cabinet to the thermal blanket. A temperaturesensor is mounted at the egress of the cabinet housing to measure theheated air for purposes of controlling the heater unit within thehousing. The flexible conduit is replaceable and connects to anappropriate coupler port on an inflatable thermal blanket. The blanketis disposable and is usually offset from the heater or source cabinet bya distance of approximately 24 to 36 inches of flexible hose length. Thetemperature sensor that is within the cabinet is physically andthermally isolated from the inflatable blanket by the hose and alsofrequently by interspaced components such as filters and connectors.

The flexible hose diameter is typically 2½ inches and the air flowvelocity is from a range of 1200 to 2000 feet a minute. The temperatureof the warm air delivered to the flexible hose ranges from approximatelyambient temperature to 48 degrees Centigrade. If the room temperature isabout 20 degrees Centigrade, there is a drop of about 4 degreesCentigrade that can occur at the highest delivered air temperature asthe air flows in the hose to the thermal blanket. This temperature drop,however, is highly dependent on not only the room temperature but alsoany turbulence generated in the hose air flow due to bends in the hose.Additional descriptions of thermal blankets can be found for example inU.S. Pat. Nos. 5,324,320, and 4,660,388.

The prior art is still seeking to improve the warming air apparatus foraddressing the issue of hypotherapy in patients undergoing surgery andto further assist in the re-warming process after surgery or prolongedexposure to cold environment.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention provides a fluid blanket warming system or thermalblanket system that can be applied to a patient to address hypothermiaand includes a blanket unit made of a light weight material such asplastic and/or plastic and paper having an approximately hollow core toform a plenum chamber for the receiving of a gas such as heated air. Acoupling port is provided to enable the admission of the gas from a heatsource. Generally, the heat source is in a portable housing cabinet thatsupports a heater unit for heating the gas and a blower unit forproviding forced air to the heater unit. A control circuit controls thetemperature of the heater unit and the air can be filtered as it entersinto the cabinet and also as it leaves the cabinet. A flexible conduitcan be removably connected to a port on the cabinet housing for thedelivery of the heated gas to an inflatable blanket unit. The inflatableblanket unit can come in various configurations and shapes and caninclude segmented or channel sections to assist in erecting the blanketwhen it is heated. The inner surface of the thermal blanket adjacent tothe patient will be porous to thereby pass the thermally controlled airto the appropriate application of the patient's body. Regardless of theparticular configuration or construction of the thermal blanket, it willhave a coupling port for removable connection with the flexible conduit.

A temperature sensor unit is mounted adjacent the thermal blanket unitand is in direct contact with the heated gas received from the heaterunit to provide a temperature signal that is representative of theheated gas, such as air, as it is delivered to the thermal blanket unit.The control circuit thereby can drive a heater unit and blower unitwithin the cabinet to provide a pre-determined temperature for thepatient which will take into account any temperature loss from theheater unit across the flexible conduit to the thermal blanket.

In one embodiment of the invention, the temperature sensor unit can bemounted within a coupler that can connect to the coupling port of thethermal blanket. The temperature sensor unit can include a heatconductive support member extending across the flow path of the heatedgas so that the temperature sensor can accurately respond to the actualtemperature. This heat conductor member can be in the form of a crossarm configuration that is structurally formed from a plastic resinsubstrate cladded with a heat conductive metal, such as copper,stainless steel, nickel, etc. The temperature sensor unit can be mountedat the inter-connection or junction of the arm members and since theheat conductive arms extend across the flow path, it can accuratelyaverage the temperature regardless of laminar or turbulent flow at theentrance to the thermal blanket.

An alternative embodiment of the invention can have the temperaturesensor unit mounted directly on a coupler that can be removably attachedto a thermal blanket rather than having it attached to a coupler on aflexible conduit.

A further alternative embodiment can have the temperature sensor unitdirectly mounted on the thermal blanket.

In an embodiment of the invention, a conduit unit for fluidlyinterconnecting a thermal blanket with a housing having a heater unitcan comprise an elongated flexible conduit with a first coupler at oneend of the conduit configured for removable connection to the heaterhousing and a second coupler at the opposite end of the conduitconfigured for removable connection to the air blanket or thermalblanket. A temperature sensor unit is mounted to sense the temperatureof the air heated by the heater unit as it exits the second coupler. Anelectrical connector can extend from the temperature sensor unit throughthe first coupler and can have an end or terminal portion adapted to beelectrically connected to transmit a temperature signal from thetemperature sensor unit to a control circuit so that the heater unit canbe controlled to a pre-determined temperature for a patient.

Finally, a second temperature sensor can also be mounted to provide aredundant measurement adjacent the first temperature sensor and a safetyalarm circuit can shut off the air warming system, if the temperaturelevel extends beyond predetermined limits.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of this invention, as well as its objects andadvantages, will become readily apparent upon reference to the followingdetailed description when considered in conjunction with theaccompanying drawings, in which like reference numerals designate likeparts throughout the figures thereof, and wherein:

FIG. 1 is a perspective view of a fluid or thermal blanket warmingsystem with a partial cross sectional view of the thermal blanket;

FIG. 2 is a partial cross-sectional view of an air warming system of theresent invention;

FIG. 3 represents a partial cross-sectional view of the coupling of theflexible conduit to a coupling port of a thermal blanket;

FIG. 4 represents a cross-sectional view of a temperature sensor andhousing as shown in FIG. 3;

FIG. 5 is a schematic diagram of a control circuit;

FIG. 6 is an elevated view of an alternative embodiment of the heatconductive support member for the temperature sensors;

FIG. 7 is an expanded view of a portion of FIG. 6;

FIG. 8 is a perspective view of an alternative embodiment of the presentinvention disclosing the temperature sensor units mounted on a thermalblanket;

FIG. 9 is a cross-sectional view of the coupler port of the embodimentof FIG. 8; and

FIG. 10 is a side view of another embodiment of the temperature sensorunit mounted in a removable coupler unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled inthe art to make and use the invention and sets forth the best modescontemplated by the inventors of carrying out their invention. Variousmodifications, however, will remain readily apparent to those skilled inthe art, since the general principles of the present invention have beendefined herein specifically to provide an improved temperature sensorunit for a fluid warming system that can be applied to a flexibleconduit, a coupler, and a thermal blanket.

The present invention recognizes that the temperature measurement whichis most important in a fluid blanket warming system for a patient suchas an air blanket or thermal blanket warming system is the temperaturein the proximity of the patient's skin. The present invention is anattempt to approximate that temperature by measuring the heated air asit is delivered to the thermal blanket in an economical manner. Whilethe present invention is disclosed with a conventional heater unit forheating ambient air, it can be recognized that the heating of othergases that may have a treatment impact upon the patient is alsopossible. The present invention discloses a schematic form of a heatsource and more specifics can be found in the inventors' co-pending U.S.Pat. No. 5,785,723, filed on Oct. 23, 1995, which is incorporated hereinby reference.

The present invention is primarily designed to provide an improvement inthe treatment of hypothermia which occurs when a patient's body coretemperature drops below 36 degrees Centigrade. A large percentage ofpatients undergoing operative procedures can become hypothermic. Some ofthe factors that contribute to this condition include the cold operatingroom environment that is favored by surgeons, the anesthetic drug effectand the consequences of opening up of a body cavity of a patient. Someof the adverse consequences of hypothermia can include coagulopathy,haemodynamic instability, immunal depression, shivering and discomfortof the patient, altered drug effect, and postoperative nitrogen wasting.

Referring to FIG. 1, a fluid blanket warming system 2 is disclosed. Aschematic cross-sectional view of a blanket unit 4 is disclosed. Theblanket unit 4 is sometimes referred to as a thermal blanket, inflatableblanket or air blanket and can be subjectively configured to addresssubstantially all or selected portions of a patient's body. The blanketunit 4 can be configured with seams and can have air slits or holes onthe underside to deliver the fluid such as heated air or other gases tothe patient when inflated. Generally, the blanket unit 4 provides an airplenum of approximately a hollow core for receiving the heated air anddistributing it to the patient's body. Frequently, the air blanket isdivided, however, into segments or conduits to assist in erecting theair blanket as a canopy across the patient's body. The specific form ofthe blanket as it is adapted to a portion of the patienty's body is nota feature of the present invention and numerous different examples existand are well known by persons of skill in this field. Thus, the blanketshown in FIG. 1 is for schematic purposes only and does not representany limitation to the air blankets or thermal blankets that can beutilized in the present invention.

The flexible conduit 8 is usually formed of a flexible plastic materialthat is corrugated and has a first coupler 10 at one end of the conduitconfiguration, and a second coupler 12 at the other end of the conduitconfiguration. A heat source 14 includes a heater housing or cabinet 16that is mounted for portability with wheels at the bottom. The upperportion of the housing 16 supports a console 18 with operatortemperature controls 20.

Referring to FIG. 2, the console 18 includes an inlet port 22 with afilter 24 for drawing air into the cavity of the console 18. A blowerunit 26 creates a positive pressure to provide air to a heater unit 28.In the embodiment of FIG. 2, ambient air is being used as the heatedfluid for application to the thermal blanket 4. It is possible, however,to provide other gases, if desired. Various configurations of blowerscroll compressor, fans, etc. can be used to provide a positive airpressure. Likewise, the heater unit can also have differentconfigurations than the resistance heater coils shown.

Downstream of the heater unit 28, a gas filter 30 can be positioned, andthe conduit from the filter 30 can be connected to a coupler 32 on theconsole 18. The second filter 30 provides extra filtration but could beeliminated, if desired. The coupler 32 is permanently mounted on theconsole 18, and the first coupler 10 on the flexible conduit 8 can beremovably connected to coupler 32.

A control circuit 34 is connected, respectively, to the blower unit 26,the heater unit 28, and a first temperature sensor unit 36. In a firstembodiment, the first temperature sensor unit 36 can be mounted within ahousing in the form of a coupler 12, as seen in FIGS. 3 and 4.

A second temperature sensor unit 38 can also be mounted on the housingof the second coupler 12 and connected to the control circuit 34 toprovide a backup or redundancy for safety purposes, as will besubsequently described.

As shown in FIG. 2, the second sensor unit 38 can have an exteriorelectrical connector line 40 that can be mounted by plug into areceptacle on the exterior of the console housing 18. Also, as shown inFIGS. 3 and 4, the first sensor unit 36 is connected to an electricalconnector line 42 that can travel along an interior of the flexibleconduit 8. As can be appreciated, the electrical connector line 40 canalso be mounted to extend along the interior of the flexible conduit 8and, if desired, they can be fastened or adhered to the internal surfaceof the conduit 8. As shown in FIG. 2, the connector line 42 from thefirst sensor unit 36 can connect with an appropriate plug or receptaclein the coupler 32 on the console 18 for connection with the controlcircuit 34.

By providing the first sensor 36 and the second sensor 38 in the secondcoupler 12, the temperature of the heated air, as it is delivered to thethermal blanket 4, can be accurately measured. Any bends in the flexibleconduit 8 that may effect a temperature drop, will occur upstream of thesecond coupler 12 and heat loss from the flexible conduit 8 will beaccounted for.

Since the temperature measured by the respective sensors 36 and 38 canbe sensitive to their particular location in the cross-sectional airflow, the present invention provides a mounting structure 44 which can,for example, comprise a plastic resin substrate 48 that is clad with ametallic thermally conductive surface 46, such as copper, nickel,stainless steel, etc. The substrate 48 of the mounting structure couldbe of the same material used for a printed circuit board with a coppercladding adhering over the surface. In the preferred embodiment, themounting structure has the configuration of an X-shape with supportingarms extending diametrically across the cross-section air flow tothereby provide an average air flow temperature at the position of thesupporting arms. As can be appreciated, the turbulence generated withinthe flexible hose and the possibility of laminar air flow can beneutralized by the X-shaped configuration so that the temperaturemeasured will represent the mean average air temperature delivered tothe thermal blanket 4.

The first sensor unit 36 and the sensor unit 38 may be any electrical orelectronic device for temperature sensing, such as a thermal couple,thermistor, resistive temperature device (RTD), semiconductordio-junction, or integrated circuit temperature sensor with and withoutintegrated controller or signal conditioner. In the preferred embodimentshown herein, the first and second sensors are thermistors mounted atthe junction or central point of the arms of the mounted structure 44.

As can be appreciated, one of the arms of the mounting structure canactually be patterned with electrical connector line traces toelectrically connect the thermal sensors to leads of a three-conductorcable. That is, three separate line traces could be used for providingconnections for each of the respective first sensor 36 and second sensor38. By use of a printed circuit substrate, an economical means ofproviding a rugged sensing structure, while also providing means formaking an electrical connection to the sensors by cladding a heattransmitting metallic material, can be accomplished. FIGS. 6 and 7 showan arrangement of providing electrical connector lines 50, 52, and 53for respective sensor units on the mounting structure 44. The threeconnectors provide power on line 53 and receive output signals on,respectively, lines 50 and 52.

Another embodiment of the present invention is disclosed in FIG. 8 inthe form of a thermal blanket 54 having a coupling port 56 of acylindrical plastic configuration. Mounted within the coupling port 56is a temperature sensor mounting structure 58 of a configuration, suchas shown in FIGS. 6 and 7 or FIG. 4. A sensor unit, such as a thermistor60, can be mounted at the junction of the mounting arms. Finally,electrical connector wires 62 can be interconnected with the console 18,such as shown in the embodiment of FIG. 2, or can be simply threadedthrough the length of the conduit line for connection with an internalreceptacle adjacent the coupling port 32 and the console 18. FIG. 9discloses a partial cross-sectional configuration of a coupling port 56of the thermal blanket 54 with a coupler 64 on a flexible conduit 66.

Finally, referring to another alternative embodiment disclosed in FIG.10, a coupler unit 68 can mount a mounting structure 70 supporting asensor unit 72 with electrical line 74. Thus, the module coupler unit 68can be removably connected to both a coupler 76 on a flexible hose and acoupling port 78 on a thermal blanket.

In each of the embodiments of the present invention, a temperature ofthe heated air can be measured as it is delivered to a thermal blanket,and the individual sensor or pair of sensors on a mounting structure canreside either directly attached to the thermal blanket, integrated withthe flexible hose, or be in a separate modular coupler.

Referring to FIG. 5, one possible schematic form of a control circuit isdisclosed. Other forms of temperature control circuits can be used, ascan be appreciated by a person of skill in this field. The specificcontrol circuit 34 incorporates a proportional controller that includesan alarm system to permit a servo-controlling of the warned air to apreset temperature level that will be set by the operator or usercontrols 20 on the housing of the console 18. In this schematic, theuser control temperature setting 80 is connected to a power supply 82through a reference voltage circuit 84 which also provides excitationcurrent for the first and second sensor units 36 and 38. The referencevoltage circuit 84 can divide and buffer the power source 82 on thecontrol circuit. By providing two separate sensors 36 and 38, there is aredundancy in the system, and the control circuit 34 can thereby alsosense the air temperature through the second thermistor or sensor unit38, located in proximity to the first sensor unit 36 or thermistor tothereby provide a backup for any over temperature condition. As a safetyfeature of this control circuit, any over temperature sensed by thesecond sensor 38 or under temperature sensed by either the second sensor38 or the first sensor 36 or the opening of an over temperaturethermostat 86, which can be located in the heater housing or console 18,can turn off the blanket warming system. Thus, any of these conditionsof an over temperature or an under temperature will indicate a problemand can be utilized to automatically shut off the power to the heaterunit 28 and the blower 26 and to also further activate audible andvisual alarms in the alarm circuit 88.

The first temperature sensor 36 amplifies the sensed voltage that isproportional to the air temperature adjacent a thermal blanket that isreceiving the delivered heated air. This temperature signal is amplifiedin a first temperature sensor amplifier 90. The amplified temperaturesignal is subtracted from a set point temperature from the user controltemperature 80 by a differential amplifier or a difference amplifiercircuit 92. The resulting output difference signal is provided to aproportional control circuit 94, and this different signal is comparedto a triangular wave that is generated to provide a pulse widthmodulated (PWM) signal whose duty cycle is proportional to thedifference in the output temperature and the set point temperatureprovided by the user control temperature 80. This WPM signal is thenapplied to a solid state power switch circuit 98 through an opticalisolator 96. The power switch circuit 98 delivers appropriate pulses tothe heater unit 100.

An alarm detection circuit includes under temperature comparator 102,under temperature comparator 104, and over temperature comparator 106.The output of these comparators 102, 104, and 106 are output togetherand inverted to be coupled to a reset input of a latch circuit 108.Additionally, the voltage across the thermostat 86 is also applied tothe latch reset through an optical isolator 110. If either the firstsensor thermistor 36 or the second sensor thermistor 38 senses a verylow temperature, which may occur in the case of an open sensor or thesecond sensor 38 senses an over temperature, or if the thermostat 86itself mechanically breaks or opens, the latch circuit 108 is reset andopens a second solid state power switch circuit 112 that is alsooptically isolated by an optical isolator 114. The power switch circuit112 is in series with the heat control power switch circuit 98, and thepower switch 112 controls power to the blower unit 116, as well as theheater 100, and has the capacity of shutting down the entire warmingsystem until this alarm condition is corrected, and the warming systemis reset by turning off the power and turning the power back on. Thethermostat 86 is in series with both of these solid state power switches112 and 98 and can positively interrupt power to both the heater unit100 and the blower unit 116. The output of the latch circuit 108 canalso turn on a transistor to activate both audible and visual alarms inan alarm circuit 88.

While applicants have chosen a preferred control circuit, theembodiments of the present invention can also be operated withalternative control circuits.

Those skilled in the art will appreciate that various adaptations andmodifications of the just-described preferred embodiment can beconfigured without departing from the scope and spirit of the invention.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention may be practiced other than as specificallydescribed herein.

What is claimed is:
 1. A blanket warming system for a patientcomprising: a blanket unit having an approximately hollow core forreceiving a gas and a coupling port to enable the admission of gas; aheater unit for heating the gas; a blower unit for forcing gas to theheater unit; a control circuit for controlling the temperature of theheater; a conduit for delivery of the heated gas to the blanket unit; atemperature sensor unit mounted adjacent the blanket unit and in contactwith the gas exiting the conduit from the heater unit to provide atemperature signal, representative of the heated gas delivered to theblanket unit, to the control circuit whereby a heater unit can becontrolled to a predetermined temperature for a patient; and a couplerfor connecting the conduit with the blanket unit, wherein the couplerhas a housing for connection with the coupling port and a heatconductive member extending across a flow path of the heated gas.
 2. Theblanket warming system as in claim 1, wherein the heat conductive membermounts the temperature sensor.
 3. The blanket warming system as in claim2, wherein the heat conductive member has a plurality of arm memberswith the temperature sensor mounted at an interconnection of the armmembers.
 4. The blanket warming system as in claim 1, wherein the heatconductive member has a plastic resin substrate and is clad with a heatconductive metal.
 5. The blanket warming system as in claim 4, whereinthe temperature sensor unit iselectrically connected to a portion of theheat conductive metal.
 6. The blanket warming system as in claim 1further including a second temperature sensor unit mounted adjacent theblanket unit and connected to the control circuit.
 7. An improved airwarming system for providing a controlled temperature of air to an airblanket comprising: a housing with an inlet for ambient air; a heaterunit for heating air in the housing; a blower unit for forcing air tothe heater unit; a control circuit for controlling the temperature ofthe heater; a remote temperature sensor unit for mounting adjacent theair blanket to provide a temperature signal representative of theaverage temperature of the heated air delivered to the air blanket tothe control circuit whereby the heater unit can be controlled to apredeterminedtemperature for a patient; and a coupler for connectingwith the air blanket, wherein the coupler has a housing for connectionwith the coupling port and a heat conductive member extending across aflow path of the heated air.
 8. The air warming system as in claim 7,wherein the heat conductive member mounts the temperature sensor.
 9. Aremote temperature sensor unit for providing a measurement of warm airto be delivered to a patient by an air blanket connected to a heaterunit, comprising: a temperature sensor for providing a temperaturesignal; a heat conductive member having a plurality of arm members withthe temperature sensor mounted at an interconnection of members; and asupport member configured for direct connection to the air blanket andsupporting the temperature sensor to measure the temperature of the warmair as it is delivered to the air blanket.
 10. The remote temperaturesensor as in claim 9, wherein the heat conductive member has a plasticresin substrate and is clad with a heat conductive metal.
 11. The remotetemperature sensor as in claim 10, wherein the temperature sensor unitelectrically connected to a portion of the heat conductive material. 12.The remote temperature sensor as in claim 11 further including asecondtemperature sensor unit mounted adjacent the air blanket unit andconnected to the control circuit.